1. Field of the Invention
The present invention relates to a method for the manufacture of a food material containing high quantities of cysteine. In this method, a yeast extract is prepared from yeast cells that contain γ-glutamylcysteine and the extract is concentrated by controlling the temperature to be not greater than 60° C. to prepare a food material in a liquid form, wherein the concentration of solids is at least 10% and the resulting food material is maintained at 70 to 130° C.
2. Discussion of the Background
Cysteine and cystine, which is a disulfide of the oxide-type of cysteine, are used to improve the taste of food. JP-A-10-136883 discloses a method where food is dipped into an electrolyte solution containing cysteine and cystine to suppress the color change of food to brown. JP-A-10-136883 also discloses that cystine is reduced to cysteine in a reduction electrode and that a brown dye, quinine, produced by an enzymatic oxidation is suppressed by cysteine. Therefore, to suppress discoloration of food by using cystine, a troublesome operation of production of cysteine by reduction is necessary.
Japanese Patent No. 3246064 discloses using cysteine for the manufacture of dried fish. According to that disclosure the dried fish, in which a sulfur-containing compound has been added in the manufacture of dried fish from material fish, taste is enhanced and deterioration of the taste is suppressed. In addition, the effect of addition of cysteine is greater per weight than for cystine.
International Publication WO 93/08274 discloses a cysteine residue prepared by reduction of cystine residue contained in animal and vegetable protein is added to improve bread dough. As such, cysteine has a broad usable range and is highly effective for use as a compared with cystine.
Methods for manufacturing cysteine by decomposition of protein and a semi-synthetic method are known and commonly used. For the use of cysteine to meet the above-mentioned object, there has been a strong demand for a food material that contains cysteine in a high concentration. However, almost no food material containing a high concentration of cysteine has been known up to now.
Based on WO 00/30474, when a food material containing γ-glutamylcysteine (hereinafter, may be abbreviated as γ-GC) is subjected to an enzymatic treatment or to a heating treatment under a specific condition, a food material containing high amounts of cysteine and cystine is produced. Although the total productivity of cysteine (hereinafter, may be referred to as Cys) and cystine from γ-GC is mentioned, the productivity of sole cysteine from γ-GC is not provided in WO 00/30474.
As previously stated, it has been known that cysteine has a broad use and is more effective compared to cystine. In addition, an efficient production method for cysteine would be useful in industry. Enzymatic manufacturing of cysteine and cystine require an enzyme and, as such, this process has a higher cost than a heat treatment manufacturing process.
In view of the foregoing, there remains a strong demand for an improved method where cysteine is efficiently manufactured from γ-GC by a heat treatment.
Japanese Patent No. 283041 and Japanese Patent No. 2903659 attempt to satisfy this demand by providing a heat treatment process. JP 2830415 discloses that addition of a saccharide to γ-GC followed by heating results in a flavor composition having good taste and flavor like roast meat. JP 2903659 discloses that, addition of a saccharide to a yeast extract containing a certain amount of sulfur-containing compound, such as glutamylcysteine, followed by heating in the absence of fat results in a seasoning having a taste of roast meat flavor. However, Japanese Patent No. 283041 and Japanese Patent No. 2903659 do not disclose or suggest that cysteine may be efficiently prepared from γ-GC.